[BUGFIX] Respect line breaks in stdWrap.cropHTML

By using the PCRE_DOTALL (/s) pattern modifier in the cropHTML
regular expression for preserving HTML entities the dot in the
pattern will include line breaks.
Resolves: #28741
Releases: 6.1, 6.0, 4.7, 4.5

Change-Id: Idb12d85681b0304730b9d76843b8352013e88123
Reviewed-on: https://review.typo3.org/19501
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack